Method of treating 1,1,1,3,3-pentafluoropropane

ABSTRACT

A method for reducing the content of unsaturated impurities contained in 1,1,1,3,3-pentafluoropropane (R245fa), while maintaining the loss of R245fa at a minimum level. R245fa containing unsaturated impurities is contacted in a gas phase with chlorine gas in the presence of an activated carbon catalyst, thereby converting the unsaturated impurities to the chlorine addition compounds to reduce the content of the unsaturated impurities.

This application is a 371 of PCT/JP00/05654 filed Aug. 23, 2000.

TECHNICAL FIELD

The present invention relates to a method for treating1,1,1,3,3-pentafluoropropane (R245fa). Particularly, this inventionrelates to a method for reducing the content of unsaturated impuritiesincluding halogenated hydrocarbons having an unsaturated bond(hereinafter referred to as unsaturated impurities) such as1-chloro-3,3,3-trifluoropropene (R1233zd) contained in R245fa.

BACKGROUND ART

R245fa is an essential substance having extensive uses including areplacement for 1,1-dichloro-1-fluoroethane (R141b) which is used ase.g. a foaming agent. As disclosed in WO 96/01797, a method forproducing such R245fa is known as an industrially effective method,wherein 1,1,1,3,3-pentachloropropane (R240fa) is fluorinated in a liquidphase, preferably, in the presence of an antimony catalyst.

However, it is known that R245fa produced by the above-mentioned method,in many cases, contains a total amount of from 300 to 20,000 ppm(weight) unsaturated impurities such as 1-chloro-3,3,3-trifluoropropene(R1233zd), 1,3,3,3-tetrafluoropropene (R1234ze),1,2-dichloro-3,3,3-trifluoropropene (R1223x),1-chloro-1,3,3,3-tetrafluoropropene (R1224zb),2-chloro-1,3,3,3-tetrafluoropropene (R1224xe) and2-chloro-3,3,3-trifluoropropene (R1233xf).

The specification of the Panel for Advancement of Fluorocarbon Test(PAFT II) stipulates that the above-mentioned unsaturated impurities,namely halogenated hydrocarbons having an unsaturated bond, should bereduced to not more than 20 ppm in a total amount.

However, among these unsaturated impurities, there are so many compoundshaving boiling points close to that of R245fa which is an objectivecompound. Therefore, it is difficult to separate these compounds fromR245fa by a usual distillation treatment. Particularly, it is difficultto separate R1233zd from R245fa by means of distillation. If theconcentration of R1233zd is reduced by such distillation to the limitingpoint stipulated by the above-mentioned PAFT II, the distillation yieldof R245fa is extremely lowered, which will lead to a large increase inits production cost.

In general, as a method for separating a saturated halogenatedhydrocarbon from unsaturated impurities such as unsaturated halogenatedhydrocarbons having physical properties similar to those of thesaturated hydrocarbon, a method has been recommended wherein a certainextent of separation is carried out by means of distillation, and then,the remaining unsaturated impurities are removed by means of a chemicalmethod. Heretofore, such various chemical methods have been proposed.For example, U.S. Pat. Nos. 2,999,855 and 4,129,603 disclose anoxidation method using aqueous potassium permanganate as an effectivemethod.

In addition, European Patent 370,688 discloses a decomposition method ofunsaturated impurities in a gas phase using a metal oxide such ashopcalite. Further, JP-A-5-32567 discloses a method wherein unsaturatedcompounds are reacted with chlorine gas in the presence of a catalystsuch as γ-alumina and activated carbon to convert unsaturated compoundsto their chloride compounds.

Further, WO97/37955 discloses a method wherein unsaturated impuritiessuch as the above-mentioned R1233zd contained in R245fa are removed bychlorination with chlorine gas under light irradiation.

However, those conventional methods have the following disadvantages andthus can not be satisfied. Namely, the method using an aqueous solutionof potassium permanganate disclosed in U.S. Pat. No. 2,999,855 haveproblems from an industrial viewpoint as described below: Potassiumpermanganate is relatively expensive; Disposal treatment of manganese,heavy metal, compound, is required. The objective saturated halogenatedhydrocarbon is moved to an aqueous solution phase of potassiumpermanganate, which will lead to the loss of the saturated halogenatedhydrocarbon.

Further, in the method disclosed in the European Patent 370,688, a lifetime of the metal oxide is relatively short such as 204 hours atlongest, and the activity of the metal oxide is also not sufficient,because the unsaturated impurities to be removed remain in substantialquantity even after carrying out the method.

Further, JP-A-5-32567 discloses a method in a broad concept wherein theunsaturated impurities are reacted with chlorine gas in the presence ofthe catalyst such as γ-alumina and activated carbon to convert them totheir chlorinated compounds, which will be then removed. However,R245fa, an objective compound in the method of the present invention,has a relatively low stability against an alkali in comparison with thecompounds disclosed in said patent. Therefore, their dehalogenationreactions are likely to occur, and at the same time, their chlorinationreactions are also likely to occur in the presence of chlorine gas.Accordingly, it can not be expected by those skilled in the art whetherthis method is applicable to a case of R245fa.

Further, in the method disclosed in WO97/37955, wherein the impuritiesare removed by chlorination using chlorine gas under irradiation oflight, it is difficult to control such reaction due to aphotochlorination reaction. As a result, byproducts caused by thechlorination of R245fa are generated in relatively large amount. Forexample, the results shown in Table 1 of the Example shows that R235fa,a chlorinated compound of R245fa, will be generated in an amount of notless than 1%, when R1233zd, an unsaturated impurity, is reduced to notmore than 100 ppm. Further, when the fluorinated compound which isobtained by the reaction of R240fa with hydrogen fluoride is employed,it is required to remove hydrogen fluoride before the above chlorinationreaction, since the light irradiation lamp made of glass is corroded bythe remaining hydrogen fluoride.

The object of the present invention is to provide a new effectivetreating method of R245fa wherein the amounts of R1233zd and/or theabove-mentioned other unsaturated impurities are reduced by convertingthem to other harmless compounds, while the loss of R245fa, an objectivecompound, is maintained at a minimum level during its treatment.

The another object of the present invention is to provide a neweffective treating method of R245fa wherein R1233zd and/or theabove-mentioned other unsaturated impurities contained in R245fa areconverted to other harmless compounds, which are then removed, wherebythe purity of R245fa, an objective compound, can be increased.

DISCLOSURE OF THE INVENTION

The present invention, which has been made to attain the above-mentionedobjects, is to provide a method for treating R245fa, which comprisescontacting R245fa containing unsaturated impurities including R1233and/or other halogenated hydrocarbons having a unsaturated bond in a gasphase with chlorine gas in the presence of an activated carbon catalyst,whereby said unsaturated impurities are converted to the chlorineaddition compounds to reduce the content of said unsaturated impurities.

In accordance with the present invention, when R245fa is contacted in agas phase with chlorine gas in the presence of an activated carboncatalyst, preferably, an activated carbon catalyst having an ash contentof not more than a particular value, the side reactions can besuppressed at a minimum level in comparison with a case wherein othercatalysts such as alumina are employed. The above side reactions aresuch that R245fa is subjected to a dehydrohalogenation reaction toproduce an unsaturated compound, and that R245fa itself is chlorinatedto produce chlorinated byproducts such as R235fa. These facts are newlyfound by the present inventors, and the present invention is based onsuch facts.

BEST MODE FOR CARRYING OUT THE INVENTION

The details of the present invention will be described with referring toExamples in the following.

R245fa to be treated by the present invention contains unsaturatedimpurities including chain or cyclic halogenated hydrocarbons having anunsaturated bond such as a double bond and a triple bond between theircarbon atoms. Such unsaturated impurities include R1233zd and/or one orat least two kinds of R1234ze, R1223xd, R1224zb, R1224xe, R1233xf, acis- or trans-type isomer thereof. The amount of the unsaturatedimpurities contained in R245fa varies depending on their productionmethods, and is preferably from 200 ppm to 5 wt %, more particularlyfrom 200 ppm to 1 wt %.

R245fa containing such impurities can be produced by various methods.Among them, is preferred the method wherein R245fa is obtained byfluorination of 1,1,1,3,3-pentachloropropane in a liquid phase withhydrogen fluoride in the presence of an antimony catalyst.

When R245fa to be treated in the present invention contains largeamounts of unsaturated impurities therein, it is preferred to removethem previously by usual distillation, whereby the total amount of suchunsaturated impurities will be preferably reduced to not more than 5 wt%. The amount of each component of the unsaturated impurities is usuallyfrom 200 ppm to 1 wt %. It has been found that the total amount ofunsaturated impurities after the treatment of the present invention canbe reduced to not more than 150 ppm, particularly not more than 100 ppm.

The activated carbon catalyst to be employed in the present invention isnot limited so long as it has property of absorbing R245fa and chlorine.However, it is preferred to use the activated carbon catalyst having alarge surface area and excellent in acid resistance and halogenresistance. For example, coconut husk activated carbon, lignin activatedcarbon, coal activated carbon or petroleum activated carbon ispreferably employed. Before the activated carbon catalyst is used, it ispreferably contacted with e.g. chlorine gas to remove functional groupssuch as carbonyl groups existing on its surface, since they may impairthe activity of the catalyst.

In the present invention, it has been found that an activated carbonhaving small amounts of ash content is preferred to reduce thegeneration of the above byproducts, since the ash content in theactivated carbon catalyst is concerned with the byproducts generated bye.g. dehydrohalogenation reaction of R245fa which is an objectivecompound. The ash content is preferably not more than 10 wt %,particularly preferably not more than 5 wt %. Herein, the ash content inan activated carbon is obtained in the following way. Namely, this iscalculated by the method described in JIS K1474 (1991)-9.

In the present invention, the procedure in which R245fa containing theunsaturated impurities is contacted with chlorine gas in the presence ofan activated carbon catalyst may be either of a fixed bed or a fluidizedbed, and the particle size of the activated carbon is suitablydetermined depending on a reaction apparatus to be used.

The contact ratio of R245fa containing the unsaturated impurities tochlorine gas is preferably such that chlorine gas is from 1 to 100,000mol, preferably from 1 to 10,000 mol, particularly preferably from 1 to1,000 mol per mol of the unsaturated impurities contained in R245fa. Toomuch amount of chlorine gas is not preferred since the substantialamount of R245fa to be treated may be lost. When R245fa is contactedwith chlorine gas, an inert gas such as nitrogen gas may be exist at thesame time.

The temperature at which chlorine gas is contacted is preferably with inthe range from the temperature at which an addition reaction of chlorineto the targeted impurities is carried out, and a chlorination and adecomposition of R245fa to be treated can be suppressed. Thus, suchtemperature is preferably within the range from the temperature at whichR245fa and chlorine gas exist substantially in the gas states to 400°C., and is particularly preferably from 50 to 300° C.

The contact time may vary depending on the kind of the activated carboncatalyst to be employed and the amount of chlorine gas to be contactedwith R245fa, and is preferably from 0.01 to 600 seconds, particularlypreferably from 0.1 to 180 seconds.

While the contact pressure is not particularly limited, so long asR245fa to be treated and chlorine gas are not liquefied in the reactionprocedure, and it is preferably from a little reduced pressure to 10kg/cm² (gauge pressure).

In accordance with the treatment by the present invention, theunsaturated impurities such as R1233zd, which has a boiling point closeto R245fa and are difficult to separate from R245fa, are converted tochlorine addition compounds, whereby the content of the unsaturatedimpurities can be reduced enough to be used as it is for some purposes.Further, in some cases, the resulting chlorine addition compounds of theunsaturated impurities have so higher boiling points than those oforiginal unsaturated impurities that it is possible to separate themfrom R245fa by means of distillation. Thus, the chlorine additioncompounds can be removed by distillation, and the resulting R245fa witha high purity can be employed in many uses.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted by these Examples. Examples 1 and3-5 are working examples of the present invention, while Example 2 is acomparative example.

EXAMPLE 1

A U-shaped flow type reactor made of Inconel 600 (inner diameter: 2.54cm, length: 600 cm) charged with 600 ml of the activated carbon catalyst(manufactured by Takeda Pharmaceutical Industry Co., trade name:Shirasagi C2X, ash content: 1.2 wt %) was immersed in an oil bath andwas kept at 200° C. Into the reactor, nitrogen gas and chlorine gas weresupplied respectively at 100 ml/min and 880 ml/min for 6 hours, wherebyunnecessary functional groups existing on the activated carbon wasremoved. Then, gasified R245fa containing the unsaturated impuritiesshown in Table 1 was supplied at a rate of 300 ml/min and chlorine gaswas supplied at a rate of 3 ml/min into the reactor and are reacted witheach other at 150° C.

The resulting reaction gas was passed through a water trap to removeacid components, and the gas components after the reaction were analyzedby FID gas chromatography. The amounts of R245fa, the unsaturatedimpurities and the chlorinated byproduct (R235fa) of R245fa before andafter the reaction were shown in Table 1 with the area % of the gaschromatograph.

N.D in Table 1 means that no component was detected by FID gaschromatography. This is also applied to the following Tables.

TABLE 1 Substance Before reaction (%) After reaction (%) R245fa 99.10099.580 R1234ze 0.124 0.001 R1233zd 0.544 N.D R235fa N.D 0.076

Further, the resulting reaction gas was recovered as 1,000 g of liquidin a trap cooled at −78° C. The recovered liquid was distilled by 2 ldistillation apparatus equipped with a packed column having the numbertheoretical plates of 15. As a result, 980 g of R245fa having a purityof 99.9% was recovered.

EXAMPLE 2

The reaction was carried out in the same manner as in Example 1 exceptthat γ-alumina catalyst was used instead of the activated carboncatalyst and the reaction temperature was 130° C. The resulting reactiongas was passed into a water trap to remove acid components, and the gascomponents after the reaction were analyzed in the same manner as inExample 1, by FID gas chromatography. The results were shown in Table 2in the same manner as in Example 1.

TABLE 2 Substance Before reaction (%) After reaction (%) R245fa 99.10097.200 R1234ze 0.124 2.225 R1233zd 0.544 0.001 R235fa N.D 0.276

EXAMPLE 3

The reaction was carried out in the same manner as in Example 1 exceptthat the reaction temperature was 200° C. The resulting reaction gas waspassed in a water trap to remove acid components, and the gas componentsafter the reaction were analyzed in the same manner as in Example 1 byFID gas chromatography. The results were shown in Table 3 in the samemanner as in Example 1.

TABLE 3 Substance Before reaction (%) After reaction (%) R245fa 99.10099.720 R1234ze 0.124 N.D R1233zd 0.544 N.D R235fa N.D 0.120

The resulting reaction gas was recovered as 1,000 g of liquid in a trapcooled at −78° C. This recovered liquid was distilled with 2 ldistillation apparatus equipped with a packed column having the numberof theoretical plates of 15. As a result, 970 g of R245fa having apurity of 99.9% was recovered.

EXAMPLE 4

The reaction was carried out in the same manner as in Example 1 exceptthat flow rate of chlorine was 30 ml/min. The resulting reaction gas waspassed in a water trap to remove acid components, and the gas componentsafter the reaction were analyzed by FID gas chromatography in the samemanner as in Example 1. The results were shown in Table 4 in the samemanner as in Example 1.

TABLE 4 Substance Before reaction (%) After reaction (%) R245fa 99.10099.050 R1234ze 0.124 N.D R1233zd 0.544 N.D R235fa N.D 0.598

Further, the reaction gas was recovered as 1,000 g of liquid in a trapcooled at −78° C. The recovered liquid was distilled by 2 l distillationapparatus equipped with a packed column having the number of theoreticalplates of 15. As a result, 950 g of R245fa having a purity of 99.9% wasrecovered.

EXAMPLE 5

The reaction similar to that in Example 1 was carried out for a longperiod of time. The components of the resulting reaction gas after 10hours and after 3,000 hours were analyzed by FID gas chromatography inthe same manner as in Example 1. The amounts of the unsaturatedimpurities, the chlorinated product and R245fa before the reaction,after 10 hours and after 3,000 hours were shown in Table 5 with the area% of the gas chromatograph.

TABLE 5 Before After 10 After 3,000 Substance reaction (%) hours hoursR245fa 99.100 99.580 99.560 R1234ze 0.124 0.001 0.001 R1233zd 0.544 N.DN.D R235fa N.D 0.0076 0.0078

Industrial Applicability

According to the present invention, the amounts of unsaturatedimpurities contained in R245fa can be effectively reduced, and the lossof R245fa to be treated can be suppressed at a minimum level.

What is claimed is:
 1. A method for treating1,1,1,3,3-pentafluoropropane, which comprises contacting1,1,1,3,3-pentafluoropropane containing unsaturated impurities including1-chloro-3,3,3-trifluoropropene and/or other halogenated hydrocarbonshaving an unsaturated bond in a gas phase with chlorine gas in thepresence of an activated carbon catalyst, whereby said unsaturatedimpurities are converted to the chlorine addition compounds to reducethe content of said unsaturated impurities.
 2. The method according toclaim 1, wherein the 1,1,1,3,3-pentafluoropropane is obtained byfluorinating 1,1,1,3,3-pentachloropropane with hydrogen fluoride in aliquid phase.
 3. The method according to claim 1, wherein the activatedcarbon catalyst is an activated carbon having an ash content of not morethan 10 wt %.
 4. The method according to claim 1 or 2, wherein the totalamount of the unsaturated impurities contained in1,1,1,3,3-pentafluoropropane to be treated is from 200 ppm to 5 wt %,and the total amount of the unsaturated impurities contained in treated1,1,1,3,3-pentafluoropropane is not more than 150 ppm.
 5. The methodaccording to claim 1 or 2, wherein the supply ratio of chlorine gas tothe unsaturated impurities contained in 1,1,1,3,3-pentafluoropropane issuch that chlorine gas is from 1 to 100,000 mol per mol of theunsaturated impurities.
 6. The method according to claim 1 or 2, whereinthe temperature at which 1,1,1,3,3-pentafluoropropane containing theunsaturated impurities is contacted with chlorine gas is within therange from the temperature at which 1,1,1,3,3-pentafluoropropane andchlorine gas exist substantially in the gas states to 400° C.
 7. Themethod according to claim 1 or 2, wherein the unsaturated impurities areconverted to their chlorine addition compounds, and then the resultingchlorine addition compounds are removed by means of distillation.